1. Reg would not limp in there almost ever so we cannot make this play against a reg.

2. Against a fish player, he will limp in many better 4x so I would not 4bet flop against him. I think your hand is quite week for that. Keep in mind they like limping in AA as well. In a limped pot, in general, don't stack off super light, especially against so much aggression from a passive player (fishy, limps pre->passive, huge VPIP-PFR gap, most likely very passive).

The only situation in which I would definitely stack off 42 here is if I knew he overplays many weak hands with aggression. Otherwise, call and play your position after he 3bets.